Improve how url-http displays status messages

Improve how url-http displays status messages

* lisp/url/url-util.el (url-display-message): New function.
(url-display-percentage): Make obsolete in favor of
url-display-message.

* lisp/url/url-http.el
(url-http-content-length-after-change-function):
Prefer 'url-display-message' to 'url-display-percentage'.
(url-http-content-length-after-change-function)
(url-http-chunked-encoding-after-change-function):
Remove ineffectual calls to 'url-display-percentage'.